Anti-glaucoma therapy and dry eye

Pubblicato il

Wednesday, 25 May 2016

Argomento

Dry Eye

Prof. Maurizio Rolando tells us about 0.2% hyaluronic acid as a protective therapy against the side effects of topical anti-glaucoma therapy

Medical therapy for glaucoma is characterised by the continuous use of one or more topical preparations that must be instilled regularly, once or several times a day, for indefinite periods of time. This has a not always positive effect on the homeostasis of the ocular surface.
In contact with the environment, subjected to constant stimuli, the surface of the eye is always at work.
It has two tasks:
- guaranteeing vision by maintaining a transparent structure of high power and optical quality
- defend what lies behind it: the retina and its complex functions.
The most dynamic part of the ocular surface system is the tear film.
The tear film has optical, protective, nourishing and lubricating functions for the ocular surface. If for some reason the tear film cannot perform these functions, the ocular surface system enters a state of crisis. If it is unable to quickly correct this difficult condition, a state of distress and subsequently disease appears.
One of the most frequent side effects of glaucoma medical therapy is the appearance of irritative complaints such as burning, foreign body sensation, fluctuating vision, and a sense of water in the eyes, associated with reddening of the eyelids and bulbar conjunctiva. These symptoms can severely impair the affected patient's quality of life, reducing or preventing normal social relationships, making common activities difficult, such as driving, especially at night, and working in front of screens, which is so frequent and indispensable today.
These symptoms, which the patient often associates with the current disease, are typical of dry eye syndromes and are actually a consequence of the drug or more often the combination of drugs being used.
Indeed, both the active ingredients and excipients, and in particular the preservatives in multidose formulations, are often irritating to ocular surface tissues and induce inflammatory phenomena capable of damaging the secreting cells of the ocular surface and inducing persistent signs and symptoms typical of dryness. Some patients also develop true forms of hypereactivity to these substances over time.
The classic presentation is that of a dry eye with a significant inflammatory component. The presence of this state of dryness and irritation, in addition to worsening the patient's quality of life and vision, reduces compliance and adherence to the therapy on the part of the patient, who perceives the irritation induced by the instillation of the medicine and tends to 'forget' it, thus jeopardising the real efficacy of the therapy over time. Experimental data also indicate a negative activity on trabecular structures by inflammation of the ocular surface .
Unable to discontinue therapy due to the risks to the optic nerve from the possible increase in eye pressure, the use of tear substitutes has become commonplace in these patients in reaction to this situation.
L'Hyaluronic acid por its ability to provide immediate comfort to the patient with tear dysfunction, it is one of the most widely used polymers in the formulation of tear substitutes. Hyaluronic acid is one of the fundamental components of connective tissues in humans and other mammals. Present in the eye under physiological conditions, it has demonstrated the ability to retain water on the surface and moisturise the epithelia of the conjunctiva and cornea and to have viscoelastic properties, i.e. the ability to change its viscosity under rubbing stress.
This property has proved very useful in the field of tear substitutes, where with the eye open, when the eye is exercising its visual functions and is most exposed to environmental threats, the instilled solution has a high viscosity that maintains a high volume of the pre-ocular tear film and good hydration, allowing increased tear stability and sharp vision. Viscosity rapidly decreases during blinking, ensuring fluidity and absence of perception.
Patients undergoing medical therapy for glaucoma tend to have an increase in the concentration of solutes contained in hyper-evaporation tears, associated with a decreased production of the glands due to altered nerve communication. It is important, in the presence of a condition of dryness associated with epithelial suffering from toxic agents, that, in addition to epithelial protection and viscoelasticity capable of rapidly improving comfort, the preparation used is not too viscous or has too long a residence time on the ocular surface, but rapidly removes, by dilution, harmful substances from both the drug itself and from cellular metabolism. In the case of hyaluronic acid the preservative-free preparation at 0.2% appears to possess the ideal balance between ocular comfort and increased tear clearance and therefore proves particularly useful in improving quality of life and adherence to topical glaucoma therapy.